Airscrew



Oct. 6, 1936. J. D. SIDDELEYv E-r AL AIRSCREW Filed Dec. 15, 1955 4 Sheets-'Sheet 1 1412 Figlzo V ATTORNEYS Oct. 6, 1936. J. D. slDDELEY ET AL 2,056,592

AIRSCREW Filed Dec. 15, 1935 4 Sheets-Sheet 2l F'z'ga OoooooooooC wir @Wa-W7 Oct. 6, 1936.

J..D. SIDDELEY ET AL AIRSCREW 4 snts-sheet 4 Filed Dec. 1s, 1935 Patented Oct. 6, 1936 UNITED STATES PATENT oFFlcE 2,058,592 Ainscanw y John DavenportV Siddeley. and Hamilton Neil Wylie, Coventry,

England,

assignors to Sir W. G. Armstrong Whitworth Aircraft, Limited, Whitley, Coventry, England Application December 13, 1935, Serial No. 54,338

In Great Britain July 3, 1934 11 claims? (ci. 17o-159) This invention relates to airscrews such as have composite blades.

The main object is to provide an improved airserew which will not be liable to flutter, will have high aerodynamic efficiency, and will be of low weight.

In ordinary airscrews the blades are liable to vibrate owing to rapid fluctuations of air pressure. In such vibrations the blades bend mainly about transverse axes lying in the direction of the width of the blade. The bending is usually accompanied by twistings which cause variations in pitch angle and consequently in air pressure, and the fluctuation in pressure is liable to syn- 115 chronizel with the bending so as to increase it. This gives rise to conditions of forced vibrationsl which cause rough running and subject the blade material to increased stress, and which in certain circumstances may be so pronounced as to amount to perceptible or even destructive fiutter of the blades.

lt is known that the twisting of the blades is mainly due to inertia forces which oppose the sudden bending of the blade under a momentary Q increase in pressure, and oppose its spring back whenthe momentary increase of pressure abates and which. cause it to overshoot the mean position. The inertia forces on any short length of blade act through the centre of mass of that E@ length whereas the resistance of the blade to bending acts along what is known as the flexural axis. If the centres of mass of each short length of blade could be arranged to lie along the ilexural axis the inertia forces would not cause twist- 35 ing of the blade, but in present-day blades oi aerofoil section and of one material, or when built up from more than one material according to common practice, the centres of mass are to the rear of the flexural axis. This disposition 40 causes fluctuations in aerodynamic pressure which increase any vibration which may have started in the blades.

Now, according to themain feature of the invention, a composite airscrew blade has its 45 leading portion formed of material having a greater density than that of material which forms, alone or with one or more lengths, or is part of,v the trailing portion, and the leading portion serves also mainly or entirely for the 50 support of the blade. For instance,l the leading portion may beof steel or aluminium alloy-and the trailingfp'ortion of wood, bakelite or other non-metallic substance oi a lower density than th'.t of the leading`portion. In this way the centreoimassotanyshortlengthotbiedcmey XIII- XIII of Figure 'l be arranged to be close to or actually on the axis oi iiexure, and it may even be slightly forward thereof. Thus the twisting due to inertia ycan be reduced or eliminated, or causedto damp out vibrations that may have started, the blade being 5 one which will rigidly resist change of form of its cross-section.

ln the accompanying drawings illustrating various constructional forms of airscrew blade embodying the principles of the invention:-

Figure 1 is a plan of a composite metal and Wood blade with parts in section; Fig. 1a is a continuation of the blade shown in Fig. l;

Figure 2 is an elevation of the leading portion of the blade as viewed from the back thereof; Fig. 2u is a continuation of the blade shown in Fig. 2; .l

Figures 3, fi and 5 are cross-sections on the lines IIL-III, IV-IV and V-V, respectively, of

Figure 1; 20

Figure 6 is a fragmentary cross-section through a blade showing a further method of joining the leading and trailing portions;

Figure 7 is a plan of a preferred form of composite blade; Fig. la is a continuation of the blade shown in Fig. '7;

Figure 8 is a part-sectional elevation thereof taken from the rear; Fig. Sais a continuation of the structure shown in Fig. 8;

Figures 9, l0, 11 and 12 vare cross-sections taken on the lines IX-IX, X-X, XI-XI and XII- XII of Figure '7, respectively; and

Figure 13 is a. cross-section taken' on the'line but indicating a small' 35 modiiication. y

Like numerals indicate like parts throughout the drawings. v In the arrangement illustrated in Figures l to 5, the leading portion 2 of the blade consists of a steel tube which is originally of uniform outside diameterl but of tapering bore so that the wall thickness increases from the tip inwards to the root. The tube is pressed to the appropriate form, the section being circular at the root 3 and changing gradually along its length to form the forward parts oi' an aerofoil as shown by the sections in Figures 3 to 5. Towards the tip the width is reduced by cutting the rear edge only at l. The root 3 is formed to be can'ied by the hub in any known manner-for example, as shown in Figure 1, a sleeve 5 having' a flanged end 5a may be fixed to the root 3 by welding, the end of the sleeve [being serrated at 6 to provide an increased length l o! weld and to improve the distribution thereof. 'Thetrailiniportlonlistormedotwoodinthe following manner. A number of individual parts 8, 8, Figures l and 5, are transversely arranged with respect to the leading portion, the grain of each part extending across the width of the blade. Each part consists of 'a piece of relatively hard wood, such as mahogany, having a substantially rectangular cross section over most of the length and havinga. circular cross section at the forward end which thus forms a peg I0. The pegs pass through clearance holes Il, Il in the rear edge of the metal portion 2 and are driven into'` and iixed, as by gluing, in holes provided in a longitudinally-extending member I2 (which may be of hard wood) housed in the rear of the metal tube 2 and iitting it closely for a substantial distance towards the tip, as shown by Figure 5. The width of the rectangular portions of the parts 8, 8, is such that they contact with each other, as shown in Figure l. Towards the tip of the blade a continuous length of wood 8a is used, this having a continuous peg portion Ina which extends with clearance through a slot IIa in the rear edge of the leading portion and'iits in a corresponding slotrin the internal member I2. Also, towards the root a continuous length of Wood 8b is used, this being secured as hereinafter described.v 'I'he parts 9, 8, 9a, 9b together form a continuous connecting rib or n 8'8 for the reception of iairing parts later described.

The internal member I2 is anchored to the root 3 so that the pull due to centrifugal'force maybe taken by the root iittings without being imposed directly on the blade. ,As shown in Figures I and 4 the internal member I2 is clamped by rivets I3, I8 between metal plates I4I4 extending towards the root and welded as shown at I5 in Figure 3 to a part-sleeve portion I8 adapted to t inside the root 8 and to act as a reinforcing plate where metal screws I1, I'I pass through the root for a purpose later described. This partsleeve Vis secured by welding to the root.

The trailing portion 8 is completed by shaped fairings I8, I8 of wood having the grain running substantially parallel to the length of the blade and secured to the connecting rib l, 8,-9a, 8b by adhesive such as glue in known manner.

The centrifugal pull due to the trailing portion is taken by metal plates or brackets of' which three are shown. The internal one I9 is lwelded to the rear of the metal portion 2 near its root and the outer ones 20, 20 are secured to the metal portion 2 and the part-sleeve I8 by the screws II, I1. The metal plates or brackets are secured to the wood laminae by bolts or tubular rivets 2l, 2l which pass through the laminae and plates and clamp these all tightly together. The Joints may be reinforced by adhesives.

In the alternative arrangement illustrated in Figure 6. the leading portion 2 and root are solid and preferably of a light alloy such as aluminium or magnesium alloy. ,The means of fitting the connecting rib 90 to the leading portion 2 consists in undercutting the rear edge of the latter as shown at 22 and the width of the undercut groove is preferably stepped down towards the tip. The connecting rib 90 'is mainly in short transverse sections as above described, these being driven tightly intoeach length of groove which they tit. Where the thickness becomes very small at the tip undercutting may be dispensed with and the wood may be held in position relative to the metal portion by thin metal sheathing of known type preferably connected only to the metal part so as to permit slight longitudinal movement relative thereto. 'Ihe wooden fairings I8, I8 are attached on each side of the connecting iin 90 as in the previous arrangement. The greatest thick- ,ness of the leading portion 2 is near its rearward stantially c-shaped part 23 which is symmetrical towards its root and bent to be of partial aerofoil section over the rest of its length towards the tip. It is formed with inwardly-extending flanges 24,24 which are bent to lprovide spaced ianges 25, 25. Actually, in the arrangement illustrated in Figures 9 to 11, the iianges 24, 25 are provided by separate angle parts welded at 26 to the ends of the C-shaped portion 23, linstead of being formed integrally therewith. A1- ternatlvely, as shown by Figure 13, they could be replaced by Z-shaped pieces 21 welded at 26 to the C-shaped part 23, these pieces providing the flanges 24 and 25.

In the present instance the hub sleeve 5 is shaped to t in the interior of the root of the C-shaped part, as indicated at 28 in Figure l1 particularly, and one wall of the sleeve is secured by rivets 29 to the packing piece 30 and to the ilanges 24. The hub sleeve 5 carries an anti-friction thrust bearing 3| disposed adjacent its ilange 5a to facilitate feathering of the blade.

The connecting rib 90 of the trailing portion is in this case built-up of three lamnae, an internal one 32 glued between two laminae 33. The latter, when of wood, preferably have the grain extending in the direction of the width'of the blade, and the internal one 32 preferably has the grain extending lengthwise of the blade. This connecting rib 98 extends for part of the blade length between the flanges 25, 25 into the interior of the leading portion 2 and is wedged in the leading portion, as shown by Figures 9 and 13,

' by means of a wooden bar 34.A Towards the root the intermediate portion 80 is cut away, as indicated at 35 in Figures 7 and l0, and is secured as by rivets 38 to the plates 3'I which extend between the ilanges 25. 'I'he root end of the con-A necting rib 80 and the plates 31 vare secured to the ilanges 25 by the rivets 39, and the connecting rib 90 is directly clamped against the ilanges 25 by the rivets 39. Filling-in pieces 48, 40 may be iltted over the lines of the rivet 39.

- Where the edges of the C-shaped part 23 come near together towards the tip the flanges 25 may be brought together, as from 25a onwards, and the wood fairings I8 be secured directly to the outside of them, the rib 90 being discontinued, as indicated at 90a. Preferably the flanges 24, 25 are cut short at 25h and extended by a T- piece |24 which is curved towards the rear edge of the blade, the edges of part 2 meeting to form the rear edge at the tip at 200.

Preferably the tip of the blade is loaded near its leading edge so that the centre of mass will be well forward thereof. Instead of the loading being applied by a thickening of the metal there,

' use is preferably made of metal strips 42 welded cur at times, as, for instance, by the rivets 39 in Figure 7 being an easy ilt in the flanges 25.

By means of the invention light eillcient airscrews can be built which will not be liable to utter. Furthermore, such blades canl be attached to the hub, by means which allow feathering'of the bladato give very satisfactory service.

What we claim as our invention and desire to secure by'Letters Patent of the United States is:-l

1. A composite airscrew blade built up from lengths of different materials on its leading and trailing portions, said leading portion being rigidly attached to a supporting -metalvsleeve, the material of which said leading portion is constructed being of greater density than the material of which -said trailing portion is constructed.

. 3. A composite airscrew bladev having different materials forming lits leading and trailing por'- tions, respectively, the material of which said. leading portion is constructed beingof greater density than the material of which said trailing portion is constructed, and the parts being arranged such that the centre of mass of any short portion of the blade is close to the transverse centre of the blade. i

4.4A composite airscrew blade consistingoi?v a hollow metal leading portion and a laminated trailing portion, the trailing portion being con` structed or material having a lower density than the material of the leading portion, said leading portion serving substantially wholly for the support off the blade.

5..A composite airscrew blade comprising a trailing portion formed of wooden laminations, and asleading portion constructed of material having a greater density than the material of the trailing portion. one of the laminations of said trailing portion having its grain extending transversely of the bladeand another having its grain extending longitudinally thereof, said leading portion serving substantially wholly for the support of the blade.

6. A composite airscrew blade comprising a trailingv portion formed of wooden laminations and a leading portion constructed of material having a greater density', than the material of the trailing portion, one loit the' laminations of said trailing portion having its grain extending transversely of the blade and another .having its grain extending longitudinally thereof, and said leading portion serving substantially wholly for the support of the blade.

7. A composite airscrew blade comprising a trailing portion formed of wooden laminations glued to one another and a hollow leading portion formed ot metal, one of said laminations having its grain extending transversely of the blade, and means for securing said one lamination to the leading portion. H r 8. A built-up airscrew blade having a hollow metal leading portion and a trailing portion formed of material having a lower density than the material of the leading portion, said trailing portion comprising a plurality of laminations,

one of said laminations extending into the interior of said leading portion, and means for se- 1ciiuring said one lamination to said leading por- 9. A composite airscrew .blade comprising a hollow metal leading portion, spaced parallel flanges extending from the rearward edges of said leading portion,y a trailing portion, said trailing portion being constructed of material having less density than the material -of which the leading portion is constructed, -said trailing portion having a part extending between said flanges, and means securing said extending part to said ilanges.

10. A composite airscrew blade having a hollow metal leading portion, spaced parallel anges carried by the rearward edges oi' said leading portion, a trailing portion, said trailing portion being constructed of material having lower density than the material of which the leading portion is constructed. said trailing portioncomprising a plurality of laminations glued to -one another, one of said laminations being built up of a plurality of parts glued to one another and extending into the interior of said leading portion, and means for clamping said one lamination against said parallel flanges.

11. A composite airscrew blade having a hollow ymetal leading portion, spaced parallel flanges carried by the rearward edges oi' said'leading portion, a trailing portion, said trailing portion being constructed of material having lower density than the material o! which the leading"l portion is constructed, said trailing portioncom-f prising a plurality of laminations glued, to one another, one of said laminations extending into JOHN DAVENPORT SIDDELEY. 

